The confluence theory, which hypothesizes a relationship between intellectual development birth order, and family size, was examined in a colombian study of more than 36,000 college applicants. The results of the study did not support the confluence theory. The confluence theory states that the intellectual development of a child is related to average mental age of the members of his family at the time of his birth. The mental age of the parents is always assigned a value of 30 and siblings are given scores equivalent to their chronological age at the birth of the subject. Therefore, the average mental age of family members for a 1st born child is 30, or 60 divided by 2. If a subject is born into a family consisting of 2 parents and a 6-year old sibling, the average mental age of family members tends, therefore, to decrease with each birth order. The hypothesis derived from the confluence theory states that there is a positive relationship between average mental age of a subject's family and the subject's performance on intelligence tests. In the Colombian study, data on family size, birth order and socioeconomic status was derived from college application forms. Intelligence test scores for each subject was obtained from college entrance exams. The mental age of each applicant's family at the time of the applicant's birth was calculated. Multiple correlation analysis and path analysis were used to assess the relationship. Results were 1) the test scores of subjects from families with 2,3,4, and 5 children were higher than test scores of the 1st born subjects; 2) the rank order of intelligence by family size was 3,4,5,2,6,1 instead of the hypothesized 1,2,3,4,5,6; and 3) only 1% of the variability in test scores was explained by the variables of birth order and family size. Further analysis indicated that socioeconomic status was a far more powerful explanatory variable than family size.